Funds are requested to purchase a Zeiss 10 transmission electron microscope that will be used by five NIH-supported investigators, postdoctoral fellows and students at the Proctor Foundation and the Department of Pharmaceutical Chemistry. The new TEM will replace an outdated Siemans 1A electron microscope that is increasingly difficult to maintain because of the unavailability of parts. The Zeiss 10 is a versatile microscope that will greatly facilitate the production of large numbers of high quality electron micrographs. It is easy to use and a good choice for a multi-user facility. The Zeiss 10 is especially desirable for the ongoing research projects of its proposed users because of special optional features such as its efficient rotating stage and goniometer. Experienced personnel to supervise the use of the proposed equipment are already employed at the Proctor Foundation, one indication of the strong commitment of the Foundation to maintain the electron microscope laboratory at top production. The EM facility contributes to both health-related and cell-biological projects. The administration of the Proctor Foundation assures service and space for the requested instrument for its useful life.